textproduct: Rapid City

KEY MESSAGES

- Scattered showers and storms at times through Monday.

- Seasonal and dry after Monday.

UPDATE

Issued at 951 PM MDT Sun Sep 27 2026

Current radar imagery shows thunderstorms developing over northeastern WY, fueled by corridor of 500-1000 J/kg MU CAPE. Storms will continue to develop into the overnight hours as WAA ramps up across the region. Not expecting any organized or widespread severe weather, however increasing shear combined with the marginal CAPE may support a few stronger cells capable of small hail. All in all, a cool and stormy September night on tap for much of the area with moisture advection and upslope flow contributing to fog over western SD. Chances for storms persist through Monday as upper level trof approaches the area. Sfc trof will cross the area in the afternoon with increasing upper level flow and narrow corridor of instability across western SD supporting a conditional severe threat, mainly over northwestern SD.

DISCUSSION

(This Afternoon Through Saturday) Issued at 1112 AM MDT Sun Sep 27 2026

SW CONUS upper trough will direct copious amounts of Pac moisture and embedded impulses over the Rockies and into the region. This will support a decent chance of showers and storms for much of the FA, best chances over the SD Plains. Stronger northern stream trough will then force a stronger cold front into the region Wed night, supporting a brief cool down. Moisture filled SW flow aloft with embedded impulses will continue to support rounds of showers and TS chances through Monday as low level Gulf moisture spreads west. Lead pos theta-e adv continues to support elevated showers and storms in the far eastern FA with a few light showers across scentral SD. LL moist easterly upslope flow continues to support widespread cloud cover over much of the western SD Plains, except for far NW SD. The next impulse will arrive later tonight and support another round of rain chances, mainly after midnight, with more isolated chances before given lack of appreciable forcing. Northern CONUS impulse will force a sfc trough into the FA Monday. This feature will provide the focus for afternoon/evening showers and storms, esp on the SD Plains where deeper low level moisture will be in place. Isolated strong to severe cells are possible as flow increases aloft with the approaching upper level trough, esp across NW SD. Rain chances will shift east overnight with things drying out Tues. Expect seasonal temps to continue after today with highs in the 70s most places through Wed. Deeper upper trough will advect across southern Canada and support a stronger cold front into the region by Wed night. This will allow for much drier and cooler air to shift south across the Northern Plains, with much cooler weather for Thur. However, this will be short lived as shortwave ridging is expected for the end of the week, bringing warmer but continued seasonal weather after.

AVIATION

(For the 12Z TAFS Through 12Z Tuesday Morning) Issued At 546 AM MDT Mon Sep 28 2026

Low clouds and lingering fog this morning will continue to produce flight conditions ranging from MVFR to IFR. That being said, conditions are improving to VFR conditions and will continue to improve through the late morning. VFR should last into the afternoon we well. More showers and thunderstorms will be possible this afternoon into tonight with showers diminishing Tuesday morning.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.